1. Field of the Invention
The present invention relates to an organic electro-luminescent (EL) display, and more particularly, to a top emission type organic EL display and a method for manufacturing the same.
2. Discussion of the Related Art
Generally, organic EL displays include, for each pixel region thereof, a switching thin film transistor for switching of a pixel corresponding to the pixel region, a driving thin film transistor for driving of the pixel, a storage capacitor, an anode (pixel electrode, an organic light-emitting layer, and a cathode (common electrode).
Hereinafter, a conventional method for manufacturing such an organic EL display will be described.
FIGS. 1A to 1E are sectional views illustrating sequential processing steps of the conventional organic EL display manufacturing method. The following description will be given only in conjunction with one thin film transistor included in one pixel of the organic EL display.
In accordance with the conventional method, first, a semiconductor layer 2 made of, for example, polysilicon, is formed over a glass substrate 1, as shown in FIG. 1A. The semiconductor layer 2 is then patterned such that the semiconductor layer 2 remains only in a region where the thin film transistor is to be formed.
Thereafter, a gate insulating film 3 and a conductive film for formation of a gate electrode are sequentially formed over the entire surface of the resulting structure. The conductive film is then patterned to form a gate electrode 4.
Using the gate electrode 4 as a mask, impurity ions such as boron (B) ions or phosphorous (P) ions are then implanted into the semiconductor layer 2 which is, in turn, annealed to form source and drain regions 2a and 2c of the thin film transistor.
The portion of the semiconductor layer 2, into which the impurity ions are not implanted, forms a channel region 2b of the thin film transistor.
Next, an interlayer insulating film 5 is formed over the entire surface of the resulting structure. Subsequently, the interlayer insulating film 5 and gate insulating film 3 are selectively removed such that the source and drain regions 2a and 2c of the thin film transistor arc exposed.
Electrode lines 6 are then formed on the exposed source and drain regions 2a and 2c such that the electrode lines 6 are electrically connected to the source and drain regions 2a and 2c, respectively.
Thereafter, a planarizing insulating film 7 is formed over the entire surface of the resulting structure. The planarizing insulating film 7 is then selectively removed such that the electrode line 6 electrically connected to the drain region 2c is exposed.
Next, an anode 8 is formed on the exposed electrode line 6 such that the anode 8 is electrically connected to the exposed electrode line 6.
Thereafter, an insulating film 9 is formed between the anode 8 and another anode 8 included in a neighboring pixel, as shown in FIG. 1B.
Subsequently, a hole injection layer 10, a hole transfer layer 11, a light-emitting layer 12, an electron transfer layer 13, and an electron injection layer 14 are sequentially formed over the entire surface of the resulting structure, as shown in FIG. 1C.
Next, a metal cathode 15 and an auxiliary cathode 16 are sequentially formed over the entire surface of the resulting structure, as shown in FIG. 1D. A protective film 17 is also formed over the auxiliary cathode 16 in order to prevent penetration of oxygen and moisture.
For the protective film 17, a multi-layer thin film is generally used. In this case, the protective film 17 not only effectively prevents penetration of moisture and oxygen, but also serves as a micro-cavity, thereby providing an optimally laminated structure. That is, the protective film 17 can greatly enhance the color purity of the display when the refractive index and thickness of each layer in the protective film 17 is optimized.
Thereafter, a sealant 18 is coated over the protective film 17, as shown in FIG. 1E. A transparent protective cap 19, which may be made of glass, is attached to the upper surface of the sealant 18. Thus, a top emission type organic EL display is completely manufactured.
The organic EL display manufactured in the above-mentioned manner exhibits an improvement in luminance and color purity because the protective film has a multi-layer thin film structure. However, the organic EL display exhibits degraded characteristics in terms of viewing angle because of the multi-layer thin film structure of the protective film.
That is, the conventional organic EL display has a problem in that there is a degradation in display quality because of a remarkable degradation in viewing angle caused by the multi-layer protective film, even though the multi-layer protective film provides an improvement in luminance and color purity.